Start writing some unit tests for schema verification

moor_generator/test/services/schema/verifier_impl_test.dart

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+import 'package:moor/moor.dart';
+import 'package:moor_generator/api/migrations.dart';
+import 'package:test/test.dart';
+
+void main() {
+  final verifier = SchemaVerifier(_TestHelper());
+
+  group('startAt', () {
+    test('starts at the requested version', () async {
+      final db = (await verifier.startAt(17)).executor;
+      await db.ensureOpen(_DelegatedUser(17, (_, details) async {
+        expect(details.wasCreated, isFalse, reason: 'was opened before');
+        expect(details.hadUpgrade, isFalse, reason: 'no upgrade expected');
+      }));
+    });
+  });
+
+  group('migrateAndValidate', () {
+    test('invokes a migration', () async {
+      moorRuntimeOptions.dontWarnAboutMultipleDatabases = true;
+      OpeningDetails capturedDetails;
+
+      final connection = await verifier.startAt(3);
+      final db = _TestDatabase(connection.executor, 7)
+        ..migration = MigrationStrategy(onUpgrade: (m, from, to) async {
+          capturedDetails = OpeningDetails(from, to);
+        });
+
+      await verifier.migrateAndValidate(db, 4);
+      expect(capturedDetails.versionBefore, 3);
+      expect(capturedDetails.versionNow, 4);
+
+      moorRuntimeOptions.dontWarnAboutMultipleDatabases = false;
+    });
+  });
+}
+
+class _TestHelper implements SchemaInstantiationHelper {
+  @override
+  GeneratedDatabase databaseForVersion(QueryExecutor db, int version) {
+    return _TestDatabase(db, version);
+  }
+}
+
+class _TestDatabase extends GeneratedDatabase {
+  @override
+  final int schemaVersion;
+
+  @override
+  MigrationStrategy migration = MigrationStrategy();
+
+  _TestDatabase(QueryExecutor executor, this.schemaVersion)
+      : super(const SqlTypeSystem.withDefaults(), executor);
+
+  @override
+  Iterable<TableInfo<Table, DataClass>> get allTables {
+    return const Iterable.empty();
+  }
+}
+
+class _DelegatedUser extends QueryExecutorUser {
+  @override
+  final int schemaVersion;
+  final Future<void> Function(QueryExecutor, OpeningDetails) _beforeOpen;
+
+  _DelegatedUser(this.schemaVersion, this._beforeOpen);
+
+  @override
+  Future<void> beforeOpen(QueryExecutor executor, OpeningDetails details) {
+    return _beforeOpen(executor, details);
+  }
+}